I know it starts young, but it takes time to get to the point where you keel over. Generally speaking, that’s not at age 40.
A friend of mine died two years ago from a heart attack. He was 56, which is tragic, but not that out of the ordinary.
I agree it is not common in 40-year-olds, but, sadly it happens:
“Sudden death due to arteriosclerotic heart disease was the single most important type of death in subjects aged 40 to 64 years, accounting for 20 per cent of the nontraumatic deaths.”
Link: https://www.ajconline.org/article/0002-9149(69)90450-0/fulltext
And the sudden death usually occurs during or shortly after excecise/vigorous physical activity:
https://www.mayoclinicproceedings.org/article/S0025-6196(12)62308-8/fulltext